“Recent studies suggest that coral reefs, however, are just as dependent on these fish for key nutrients that help coral grow. When fish urinate, they release phosphorus into the water. This phosphorus, along with nitrogen excreted as ammonium through the gills of fish, is crucial to the survival and growth of coral reefs.”
This study highlights a very important truth in reef keeping. Everything pees and poos in your tank. Having high phosphates isn’t desirable. It can cause algae and it can keep stony corals from properly building their skeletons. But no phosphates is also bad. On the reef proper this is often the only source of nutrients for the corals. However, in your tank you add in a lot of food so the fish pee isn’t the only source of these nutrients. Keep an eye on your phosphates but understand that you aren’t trying for a true reading of zero.
What do I recommend for phosphates in a reef tank? < 0.03 ppm should be just fine. This isn’t as hard to achieve as you might think with just water changes. If you have difficulty due to the number of fish or the type of food you can run GFO or granular ferric oxide
However, you can also use algae to your advantage by growing macro algae in your sump.
Source: Big fish — and their pee — are key parts of coral reef ecosystems | UW Today